In product development for developing a high performance product at a low cost, assume that the first objective is to improve the performance of the product and the second objective is to minimize the cost of the product. When the development is attempting to improve the first objective (i.e., improve performance), the second objective suffers (i.e., cost becomes higher). Conversely, when the development is attempting to improve the second objective (i.e., reduce cost), the first objective suffers (i.e., performance degrades). In this way, the first and second objectives cannot be improved together and are in conflicting relationship, and this relationship is called “trade-off relationship”. To improve a plurality of objectives having the trade-off relationship, multi-objective optimization techniques are well known. Please see, for example, Japanese Laid-open patent Publications Nos. 2005-70849 and 2011-103067.
Some of the known methods for displaying the results of multi-objective optimization include a scatter diagram matrix in which scatter diagrams for all different combinations of input and output variables are arranged in matrix, and a parallel coordinate plot where a horizontal axis represents input and output variables and a vertical axis represents the values of the input and output variables.
A user narrows down the values of input variables to ranges that are expected to yield user-desired values of output variables, from a scatter diagram matrix or a parallel coordinate plot, and runs a simulation within the determined ranges in order to obtain the values of the output variables corresponding to the values of the input variables falling within the determined ranges. The user is able to confirm whether the values of the output variables obtained from the values of the input variables in the determined ranges are user-desired values or not.
However, as the number of input and output variables increases, it becomes more difficult to interpret the relationships among input and output variables from a scatter diagram matrix or a parallel coordinate plot.